This application relates to the preparation of carbamates, ureas, and isocyanates using an activated ester carbonates (e.g. an ester-substituted diaryl carbonate) such as bismethylsalicylcarbonate (BMSC) as a reactant.
Monomeric carbamates, ureas, and isocyanates find substantial utility in a wide variety of applications including fine and specialty chemicals, pharmaceuticals, cosmetics, and agriculture and crop protection. Carbamates and ureas share a common structural element in which a carbonyl group is flanked by an oxygen and a nitrogen (carbamates) or two nitrogens (ureas). Isocyanates can be made by pyrolysis of a carbamate or a urea.
Commonly, carbamates and ureas are synthesized by reactions making use of phosgene gas or a solid phosgene precursor such as triphosgene in a reaction with two amines or an amine and an alcohol. The adoption of triphosgene is preferred for safety reasons, even though it costs more and is generally less reactive, requiring longer reactions at higher temperatures. However, triphosgene is only “safe” relative to phosgene itself and it is still classified as a very hazardous material that can generate hazardous decomposition products namely hydrogen chloride, chlorine, phosgene in addition to the carbon monoxide as well as carbon dioxide normally resulting from the extreme thermal degradation of organic compounds. Carbamates (also known as urethanes) can also be made from reaction of a urea intermediate with an alcohol. Dimethyl carbonate and diphenyl carbonate are also used for making carbamates and ureas, but they require long reactions times and/or high temperatures, and/or catalyst to achieve this result.